A Universal Mobile Telecommunications System (UMTS) is a third generation mobile communications system that uses the Wideband Code Division Multiple Access (WCDMA) technology. The UMTS is generally called a WCDMA communication system. The UMTS is designed with a structure similar to the structure of a second generation mobile communication system, and includes a Radio Access Network (RAN) and a Core Network (CN). The RAN is configured to process all radio related functions, and the CN is configured to process all voice calls and data connections in the UMTS and configured to implement switching and routing with external networks. Logically, the CN consists of a Circuit Switched (CS) domain and a Packet Switched (PS) domain. The whole UMTS is composed of a UMTS Territorial Radio Access Network (UTRAN), a CN and a User Equipment (UE). The UTRAN includes one or multiple Radio Network Subsystems (RNSs). Each RNS consists of a Radio Network Controller (RNC) and one or multiple NodeBs. The RNC is configured to allocate and control radio resources of the NodeBs connected or related to the RNC. The NodeB converts data streams between an Iub interface and a Uu interface, and manages some radio resources.
Considering the future competitiveness of networks, the 3rd Generation Partnership Project (3GPP) is carrying out a research on new evolved network architecture to meet future mobile network application requirements. The evolved network architecture includes System Architecture Evolution (SAE) and Long Term Evolution (LTE). An evolved access network is called an E-UTRAN. The purpose of network evolution is to provide an all-Internet Protocol (IP) based network, which has the features of low delay, high data rate, high system capacity, wide coverage, and low cost. The UMTS network and SAE network may coexist for a period of time in the evolution from UMTS to SAE. FIG. 1 shows an architecture of an evolved network in the prior art.
As shown in FIG. 1, the E-UTRAN11 is an RAN in the evolved network; the Mobility Management Entity (MME) 12 is configured to store Mobility Management (MM) contexts of the UE, for example, user ID, mobility state, and Tracking Area (TA) information, and the MME is also configured to authenticate the user; the serving gateway 13 is an entity for terminating the downlink data transmitted to an idle UE, and is configured to trigger paging and store contexts of the UE, for example, IP address and routing information of the UE. The Public Data Network (PDN) gateway 14 is an anchor point of the user plane and remains the same during the user session. The Policy and Charging Enforcement Function (PCEF) is located in the PDN gateway. The Policy and Charging Rules Function (PCRF) 15 is configured to generate a Policy and Charging Control (PCC) rule and push the PCC rule to the PCEF where the PCC rule is enforced. The MME 12 is connected to the Serving GPRS Support Node (SGSN) 16 via the S3 interface. A 2G/3G user may access the SGSN 16 via the UTRAN or the GSM Edge Radio Access Network (GERAN). The evolved architecture is compatible with 2G network and 3G network. The architecture of the evolved network is designed from the perspective of smooth evolution. In early deployment of the evolved network, LTE access network (i.e. E-UTRAN) is deployed in some places only, and not nationwide. This is called hot coverage. Outside hot coverage areas, users can access the network via the UTRAN/GERAN only. Thus, in a handover process incurred when a user moves between the evolved network and the 2G/3G network, the service continuity must be guaranteed when the domain and Radio Access Technology (RAT) are changed.
In addition, it is also important for the evolved network to be compatible with the existing networks. To protect the existing investments of the operators and fully use traditional CS entities, the prior art provides a solution for carrying CS data and signals in a PS domain in an evolved network, that is, an evolved Mobile Switching Center (eMSC) solution. In the eMSC solution, voice call services in an LTE/SAE network are uniformly controlled by the CS domain, and services from different access areas are controlled by a same eMSC, so that the voice call service continuity between the CS domain and the LTE/SAE network can be guaranteed. Nevertheless, the eMSC solution does not describe the detailed architecture of the eMSC solution and how the UE is attached to the eMSC.
A Generic Access Network (GAN) originates from Unlicensed Mobile Access (UMA), and is configured to extend the use of mobile voice and data in GSM/General Packet Radio Service (GPRS) in unlicensed spectrum technologies. For example, Bluetooth and Wireless Local Area Network (WLAN). The purpose of introducing the GAN is to use the WLAN access as a supplement in areas where a GERAN has poor coverage, so that the user can continue using the CS and PS services provided by the core network. The GAN describes how the UE accesses the GERAN (which is composed of a PS domain and a CS domain) from the WLAN and how the UE is handed over between the cellular network and the WLAN to maintain the seamless continuity of the voice and data sessions. In general, a Generic Access Network Controller (GANC) similar to a Base Station Controller/Radio Network Controller (BSC/RNC) is simulated in a WLAN IP network, and a new interface (Up interface) is introduced between the GANC and the UE. The UE is connected to the GANC via an IP transport network. The GANC is responsible for data interactions between a user plane and a control plane to access the GSM network. However, the eMSC solution is only applicable to only the connection between the WLAN and the GERAN, and seamless handover between the cellular network and the WLAN in case of dual radio. With the emergence of radio broadband technologies such as SAE/LTE and Worldwide Interoperability for Microwave Access (WiMAX), a solution for performing seamless handover between the SAE/LTE or WiMAX network and the cellular network in case of single radio (namely, single transmitter and single receiver) must be considered.